In recent years, the powder rapid prototyping apparatus and the powder rapid prototyping method have been researched and developed to fabricate a substitute item for a metal product, a prototype of a product which is placed in a high-temperature environment or in which higher strength is required, or parts of high-mix low volume production, etc.
Regarding metal powder materials, stainless steel or bronze steel has already become usable, and aluminum, titanium or the like is being researched and developed in order to further widen application.
Previously, there has been the following inconvenience regarding the metal powder materials. Specifically, oxygen or nitrogen is introduced into metal powder when the metal powder is exposed to air. Thereby, the metal powder is oxidized or nitrided, and thus a finished model becomes very fragile.
To solve this problem, the present inventors have developed a technology (Japanese Patent Laid-open No. 2011-021218) in which thin layers of metal powder is formed, and sintered or melted and then solidified in a decompressed atmosphere.
Although the technology described in the patent document above has solved, to a certain extent, the inconvenience that the metal powder is oxidized or nitrided and a finished model becomes very fragile, there are cases where even further improvement is required for some application.
Further, in the case of using the metal powder, another inconvenience caused by oxygen or nitrogen and an influence by water have also newly become a problem as described below, therefore further improvement is required together with the above cases.
(1) If water is contained in the metal powder, water vapor generated from water, or nitrogen or oxygen produced by decomposed water is introduced into the metal powder.
Further, energy of energy beam for heating use is mainly consumed for vaporizing water, and therefore, only the surface of particles melts to allow the particles to adhere to each other, and the surface of model becomes textured finish.
(2) Further, even in metal powder material that is left without being irradiated by energy beam after modeling, the composition purity is deteriorated due to oxidization or the like, and thus its reuse becomes difficult.